Category Archives: Weather Outlook

Philly Weekend Weather Outlook- 4th of July

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While I heard the TV weather people last night give a forecast of beautiful weather  for this weekend, the actual weather forecast for this weekend is anything but a certainty.  In fact, this weekend’s forecast is looking to be below average confidence.

A stalled frontal boundary will be just to our south.  Waves of weak low pressure are expected to ride along this front bringing periods of showers to Virginia, Maryland and parts of Delaware from Friday through Sunday.   Whether this front is suppressed to the south, or whether it tries to develop warm-front properties with moisture moving north of it will determine our actual holiday weekend weather.

The models are hinting that some of this shower activity may ride north of the actual frontal boundary, giving Philadelphia and even South Jersey  periods of clouds and showers during the weekend.   It doesn’t look to be a blue skies weekend, but neither does it appear to be totally cloudy or showery.  A mix of sunshine, clouds and occasional showers is most likely.  Timing of the actual showers isn’t possible at this time.  Stay tuned.

Philly Weekend Weather Outlook

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GFS forecast for early Saturday evening
GFS forecast for early Saturday evening

The models have been consistent in predicting low pressure development along a stalled frontal boundary, with heavy rain for Saturday in our area.

The models have the precipitation lifting out to the northeast on Sunday, but the amount of clearing is uncertain, since we will still be in a cyclonic wind flow.


Philly Weekend Weather Outlook

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Those of you following the past days forecast details would notice that the model forecast accuracy has not been at its best– the position and movement of the warm front has been difficult to accurately predict.

It appears that the warm front has finally moved past our area Friday morning (winds have shifted to the southwest).   There’s the possibility of some thinning cloudiness during the afternoon and maybe some breaks of sunshine.

In fact, the “maybe some breaks of sunshine” may be the forecast challenge for this weekend.

This weekend, we will be in a south to southwesterly flow of very moist and somewhat unstable air.  The models are predicting heavy rain for Saturday night and early Sunday morning.  Maybe you can hang your hat on this, maybe you can’t.

But if we assume that late Saturday afternoon into early Sunday morning will be a definite rain time frame, the rest of the weekend weather forecast is a bit more challenging.   Forecast uncertainty is high this weekend regarding details.

For Saturday, we’ll start with some clouds, maybe some breaks of sunshine, warm and humid.  High 84.  Showers and possibly some thunderstorms develop mid to late Saturday afternoon into the evening.  Rain may be heavy.

Sunday starts with lingering rain and showers, then it ends.  Thinning clouds possible in the afternoon and maybe some breaks of sunshine in the later afternoon.    High 83.

I’ll try to fine tune this during the weekend.


Friday Weather Update

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This morning’s models continue showing precipitation starting Friday morning about 8AM  and ending Friday evening.

Temperatures at the surface will be around freezing (the MOS lately has not been very accurate with temperatures).  Temperatures in the lower levels of the atmosphere will support snow through early afternoon.  Temperatures in the upper atmosphere just marginally support snow.  QPF values have increased to over 0.65+ inches for both the NAM and GFS.   With heavier precipitation rates, dynamic cooling might make temps a bit colder.

Areas to the north and west of Philadelphia are more likely to have snow accumulate.

So a messy day for Friday.  Right now it looks like much of the day it will fall as wet snow, but accumulations will be limited, especially on dark asphalt roadways.  A change to rain is likely after 3 PM.

Everything is right on the edge of being a rain event, so it would not take much for the expected snow to fall as a wet mix or just rain.  Right now, I’m betting on it coming down as snow, likely changing to rain during the mid afternoon on Friday.